This invention relates to a tool for removing material from a workpiece. The tool has a rotatable wheel with an abrasive strip thereon which is easily replaceable and on which the tension is increased during rotation of the wheel.
Grinding wheels for grinders can be formed from solid discs of abrasive material. Alternatively, a strip of abrasive material has been wrapped around a wheel or drum to provide a grinding surface upon rotation of the wheel. To enable the abrasive strip to be capable of generating precision surfaces and fine finishes on a workpiece, the abrasive strip must be held on the wheel so that it always firmly engages the circumferential surface of the wheel during rotation of the wheel irrespective of the speed of rotation of the wheel.
Because the abrasive strips are subject to heat, wear and vibration which dislodges the abrasives from the strip, the abrasive strips must frequently be replaced. The grinders themselves usually provide limited access to the rotatable wheel for changing the strip because of the presence of the machinery necessary to rotate the wheel and position the wheel along the workpiece. Guards or protective housings are frequently placed about the rotatable wheel to prevent objects from inadvertently coming in contact with the wheel and to protect the operator. Because the abrasive strips must be replaced frequently and because of limited access to the wheel it is desirable to have a wheel which provides features for making the replacement of abrasive strips easier and faster.
One previously suggested means for holding a coated abrasive laminate material (CALM) strip on such a wheel has been to form a rim on the wheel with a large recess or cavity inside the rim. The wheel has a hub for mounting the wheel on the drive shaft of the grinder. The rim has a transverse slot providing communication from the recess to the exterior of the circumferential surface of the wheel so that the two ends of the CALM strip can enter into the recess. One end of the CALM strip is fastened into the recess by an eccentric lock, which tightens through the centrifugal forces developed during rotation of the wheel. The other end of the CALM strip is brought towards the center of the wheel and wrapped around a roller so that the end of the strip is pointed outwardly from the axis of rotation. This end of the strip is attached to a metal weight having a specific mass and positioned close to the roller to provide for the maximum distance for any stretching of the CALM strip. Rotation of the wheel causes the floating mass, through centrifugal force, to provide tension on one end of the CALM strip to keep it in its proper position. A counterbalance weight is employed to offset and correct for the imbalance created by the floating mass, the roller, and the eccentric lock. A coverplate extends over the cavity inside of the rim and has a hole to permit insertion of a tool for adjusting the initial tension on the CALM strip.
This arrangement for securing a CALM strip to a grinder wheel requires the removal of the coverplate for replacing the CALM strip. Removing the coverplate is time consuming and very difficult because of the limited access to the wheel in its operating environment. In addition, the coverplate and other parts (e.g., screws or fasteners) must be set aside and retained during CALM strip replacement, and are subject to loss. Furthermore, this design requires that the trailing end of the CALM strip be wrapped around a holding pin and inserted into the flying mass assembly, while the leading end must be threaded through the initial tensioning assembly which must then be rotated by a special tool to remove excess slack of the CALM strip and apply an initial tension to the CALM strip. Such manual manipulations can be difficult, especially when access to the wheel is limited by adjacent machinery.
Mattson U.S. Pat. No. 4,823,516 discloses a cutting tool having a rotatable wheel with a removable abrasive strip thereon. Removable endpieces are attached to the abrasive strip, which are then engaged by a mechanism within the circumferential surface to apply tension on each end of the strip in accordance with the speed of rotation of the wheel. The strip tensioning mechanism is located in a cavity within the circumferential surface and enclosed by a removable coverplate. Replacing the abrasive strip requires removal of the coverplate. The endpieces must be removed from the old strip and installed on the new abrasive strip before the new strip can be installed. The coverplate then must be replaced and fastened into place.
Two U.S. patents issued to Wattles, U.S. Pat. No. 879,504 and U.S. Pat. No. 967,592, disclose a grinding or polishing wheel with a strip of flexible abrasive material detachably secured thereto. One end of the strip has an adjustable tension applied thereto, while the other end has a beaded end for retaining it in position within the wheel. The tensioning mechanisms shown in both of these Wattles patents are only partially enclosed by a coverplate, thereby allowing strip replacement without the removal of the coverplate. The arrangement in Wattles U.S. Pat. No. 879,504 requires the release of a pawl to allow the tensioning mechanism thereof to be forced against the tension of a spring into position for receiving the abrasive strip. Once aligned in its strip loading position, the tensioning mechanism is held in place by the pawl. The arrangement in Wattles U.S. Pat. No. 967,592 requires a tool to be inserted through the coverplate for positioning the tensioning mechanism for strip replacement, against the force of the tensioning spring, beneath a cutout in the coverplate adjacent the rim of the wheel.
Hunt U.S. Pat. No. 2,046,122 discloses a buffing and polishing wheel having a cushion on its circumferential surface on which an abrasive strip is mounted. Serrated endpieces are attached to the end of the strip and these endpieces are received by a tensioning mechanism in the wheel which then applies tension to the strip as a means for automatically taking up slack occurring in the abrasive strip (as a strip of coated abrasives is used, it stretches). Hunt shows the use of endpieces installed on the ends of the strip which must be compressed in order to grip the strip and hold the strip in the tensioning apparatus.
As noted in the exemplary references and devices discussed above, previous grinder strip-type tools for removing material from a workpiece required the removal of numerous parts during the replacement of the abrasive strip, which was difficult and time consuming. Each abrasive strip required the attachment of special endpieces for allowing the tensioning apparatus of the grinder wheel to engage the strip and withstand the large forces as the wheel turns at high speeds and the strip engages the workpiece.